Magnetic properties of polycrystalline FeBSi alloys with ultrafine grains

It has been found that the Curie temperature T_c and saturation magnetic induction B_s decrease with decreasing grain size while the coercivity H_c increases significantly with decreasing grain size. The observations are attributed to the specific vibrational spectrum of grain boundary atoms results in the increase of their mean square displacements and the latter may induce the magnetic disorder. The increase of H_c can be interpreted by the significant enhancement of defects density with the reduction of grain size. We also found that the optimum soft magnetic properties can be obtained when only a small amount of -Fe crystallites precipitated during well-adjusted heat treatment. This can be interpreted in terms of an additional magnetic anisotropy energy.     

Magnetic properties of nanocrystalline Finemet alloys with Co addition

This report focuses on ac magnetic properties of (Fe_0.5Co_0.5)_73.5Cu₁Nb₃Si_13.5B₉ alloy in the high temperature. The effects of replacing 50% Fe by Co in Fe_73.5Cu₁Nb₃Si_13.5B₉ alloy on the static magnetic properties have also been studied. Addition of Co leads to an increase around 110 K of the Curie temperature of the amorphous phase, much higher than Ge-containing Finemet alloy. The material has much better ac magnetic properties than Hitperm alloy. An excellent stability of initial permeability in high temperature (up to 650 K) and high frequency (up to 5 × 10⁵ Hz) can be observed with respect to the Co-free alloy.     

Magnetic and structural properties of rapidly quenched Nd-Fe-Co-Ge-B alloys

We have studied the magneto-resistive effect in bulk Y_3/4Lu_1/4Ba₂Cu₃O₇ + CuO composites prepared by the fast-sintering technique. It has been found that the composites exhibit large magnetoresistance in low magnetic fields (<100 Oe) in a broad temperature range (tens of kelvins below the critical temperature T _c). The HTSC-based composites exhibit a much higher sensitivity to weak magnetic fields at liquid-nitrogen temperature as compared to pure HTSC ceramics. By choosing a proper bias current j, it is possible to control the shape of the resistivity-magnetic field ρ(H) characteristic of the composites and to vary the parameter R ₀ = {R(H = 0) ? R(H)}/R(H = 0). Under the condition j > j _c (where j _c is the critical-current density), large values of the magnetoresistance R ₀, up to thousands percent, are obtained in the range of weak magnetic fields (tens of oersteds) at 77 K. This effect is attractive for practical applications of these composite materials as active elements of magnetic-field sensors. The sign of the magneto-resistive effect is positive in contrast to that of manganese oxides. This may be important for some devices.     

Magnetic and mechanical properties of FeSi alloys with high Si content

The chemical vapor（CVD） deposition-diffusion method was applied to prepare FeSi alloys with high silicon content up to 6.5%. In spite of various deposition and post-annealing, the sample remains α-Fe bcc structure. The cross section of the composition was analyzed to evaluate the Si content and distribution before and after annealing. The results show that the soft magnetic properties are improved by increasing the silicon content. For the samples containing about 6.5% Si, the coercivity decreases to 60 from 237.3 A/m of the original. It is also obtained that, in addition to the Si content, Si distribution has a large influence on the core loss due to the effect of resistivity. The micro-hardnesses were also evaluated along the cross-section after various annealings.     

Effect of HCl pre-treatment on corrosion resistance of cerium-based conversion coatings on magnesium and magnesium alloys

The corrosion protection afforded by a cerium conversion coating, formed by immersion in a solution containing rare earth salt and hydrogen peroxide, on pure magnesium and two magnesium alloys, AZ91 and AM50, has been studied. The effect of HCl pre-treatments on the morphology and on the corrosion resistance of the cerium conversion layer was investigated. A thicker and more homogeneous distribution of the conversion coating was obtained when the sample surface was pre-treated with acid. Higher amounts of cerium on the surface of the pre-treated samples were detected. The cerium conversion coating increased the corrosion resistance of the alloys because it ennobled the corrosion potential and decreased both the anodic and cathodic current. The acid pre-treatment further increased the corrosion resistance of the coated alloys. After five days of immersion in chloride environment the untreated samples showed localized corrosion while the chemical conversion coated samples appeared unaffected.     

Effect of heat treatment on some properties of two low-gold dental alloys

The effect of heat treatment on microstructure, microhardness, tensile properties, and corrosion behavior of two low-gold dental alloys has been studied. After quenching, specimens were heat-treated in the temperature region from 300–500°C. Microhardness, yield strength, and tensile strength showed maximum values between 350°C and 400°C, and then decreased at higher temperatures. Potentiodynamic curves revealed that nobility affects silver corrosion activity.     

Magnetic properties of nanocrystalline FeMCuNbSiB alloys (M: Co,Ni)

The magnetic properties and microstructure of nanocrystalline FeMCuNbSiB alloys (M: Co, Ni) annealed under a transverse field have been studied. Large induced magnetic anisotropy and good properties in the high frequency range were obtained in Co-rich nanocrystalline FeCo(Cu)NbSiB alloys.